Gravimetric measuring instruments like those of interest here may serve, for example, as balances and weighing modules in many areas of industry, particularly in laboratories of research and development departments, but also as weighing modules in production departments, for example in quality control. Weighing modules, as used herein, are balances in which the display and/or the data entry unit is arranged separately from the weighing cell and the weighing cell housing.
In EP 1 576 343 B1, a weighing module with a weighing cell is illustrated schematically in a sectional view. The load-transmitting member that is arranged in the load-receiving area of the weighing cell is, at its free end, configured in the shape of a truncated cone. The load receiver shown in this reference has a conical bore that conforms to this frusto-conically shaped free end. Normally, the truncated cones used for this kind of releasable connection have a small taper angle, so that even under an eccentric load the load receiver will not tip over and fall off the load-transmitting member. However, due to this small taper angle, extremely large levels of contact pressure or bearing stress occur in the areas of the contact surfaces. This type of connection is therefore only suitable for balances with small load capacities, even if the connection is made of metal. Furthermore, this type of connection can only be used if a defined orientation of the load receiver—other than a defined position of its mass center of gravity—in relation to the weighing cell is of no importance, i.e. only for rotationally symmetric load receivers or weighing pans.
Based on the foregoing issues, this type of connection is in most cases not suitable for weighing modules in industrial applications. In industrial applications, the load receiver is instead normally screwed onto the load-transmitting member. This connection method has the disadvantage that the installation and removal of the load receiver are very time-consuming, as the entire load receiver has to be turned in relation to the weighing cell. This presents a problem particularly if application-specific devices, such as for example conveyor belts, clamping devices for containers and the like, are attached to the load receiver and the spatial dimensions are so tight that these application-specific devices have to be removed first from the load receiver before the latter can be unscrewed from the load-transmitting member. Weighing modules with application-specific devices are often used in filling and checking devices of production systems for the apportioning and checking of bulk products. Such systems are in many cases designed with multiple tracks, so that a plurality of weighing modules as well as their in-going and out-going conveyor devices are arranged in parallel within a very confined space.
According to a further variant within the state of the art, the load receiver or the weighing pan is attached to the load-transmitting member by means of a screw, which is arranged along the central longitudinal axis of the load receiver and the load-transmitting member. While this allows the load receiver to be disconnected more easily from the load-transmitting member (i.e., without having to turn the entire load receiver), the hole for the screw creates a leak point in the load receiver that needs to be sealed. Such screw connections are also in many cases highly undesirable because of sanitary and cleaning concerns, as the screw is arranged on a horizontal surface and contaminants may accumulate around the screw head. It is self-evident, especially in order to meet the stringent requirements regarding the cleanliness of such production systems, for example in the food and pharmaceutical industries, that the ability to quickly install and uninstall the load receiver for cleaning is of the utmost importance.
The present invention is therefore directed to a gravimetric measuring instrument with a weighing cell that allows a load receiver to be attached to and removed from the load-transmitting member of the weighing cell in a quick and simple manner.